const React=require('react');
const ReactDOM=require('react-dom');

class Clock extends React.Component{
    constructor(props){
        super(props);
        this.state={date:new Date()};
    }
    componentDidMount(){
        this.timerId=setInterval(()=>this.tick(),1000);
    };
    componentWillUnmount(){
        clearInterval(this.timerId);
    }
    tick(){
        this.setState({date:new Date()});
    }
    render(){
        return(
            <div>
                <h1>HELLO WORLD!!!</h1>
                <h2>It is {this.state.date.toLocaleTimeString()}</h2>
            </div>
        );
    }
}
ReactDOM.render(<Clock/>,document.getElementById('page'));